Rename ConfigurablePluginBuilder to Builder in the util package.

  - This is pretty generic and can be re-used for whatever.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597630 13f79535-47bb-0310-9956-ffa450edef68
Make PluginBuilder implement Builder.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597631 13f79535-47bb-0310-9956-ffa450edef68
Add some todo comments.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597632 13f79535-47bb-0310-9956-ffa450edef68
Rename defaultValue() to defaultStringValue().

  - Also added other defaultFooValues.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1597635 13f79535-47bb-0310-9956-ffa450edef68